Document Type : Research Paper


1 Ph. D student of Accounting, Babol branch, Islamic Azad University, Babol , Iran.

2 Assistant Professor of Accounting, Faculty of Economic and Administrative Sciences, University of Qom, Qom, Iran

3 Assistant Professor, Department of Accounting, Faculty of Economic and Administrative Sciences, University of Mazandaran, Babolsar, Iran.

4 Assistant Professor, Department of Accounting, Babol branch, Islamic Azad University, Babol , Iran.


The aim of this study is to develop a comprehensive model that identifies the non-fragile variables affecting the quality of tax audit. We analyzed 511 tax files from Mazandaran province in the period spanning 2012 and 2021. Initially, through interviews with experts and literature, 64 factors affecting the quality of tax audits were identified. These factors were categorized into three groups: characteristics of taxpayers, tax auditors, and macro factors. Subsequently, the relevant data were applied to Bayesian Model Averaging (BMA), Time-Varying Parameter Dynamic Model Averaging (TVP- DMA), and the Time-Varying Parameter Dynamic Model Selection (TVP-DMS) models. Among these, the BMA model demonstrated the highest accuracy based on the error rate. After model estimation, 17 main indicators were identified as influential variables in three areas. In the realm of tax auditors, these included the quality of past period tax audits, work experience, individual or group handling of audits, auditor expertise, auditors’ use of information, auditor’s workload, conducting audits across multiple tax sources, interactions with related parties, the presence of unofficial invoices, and the use of others’ business cards. In terms of intra-company variables, accrued earning management and debt ratio were identified. Finally, macroeconomic variables impacting the quality of tax audits were found to be inflation, unofficial exchange rates, tax complexity, tax fairness, the business environment index, and the social capital index.


Factors affecting the quality of tax auditors can be divided into three groups: characteristics of taxpayers, tax auditors, and macro factors. The current challenge in evaluating factors that determine the quality of tax auditors lies in the diversity of theories and the absence of a specific, universally accepted model. On one hand, the multitude of potential explanatory variables affects the quality of tax auditors. On the other hand, this abundance makes the use of classical econometric models problematic. One method to address the uncertainty in selecting variables and choosing the appropriate model is to employ conventional techniques in Bayesian econometrics. These include Bayesian Model Averaging (BMA), Bayesian Maximum Likelihood Averaging Model (BML), Time-Varying Parameter Dynamic Model Averaging (TVP-DMA), and Time-Varying Parameter Dynamic Model Selection (TVP-DMS). Little research has been conducted in the field of tax audit quality. Furthermore, to date, there has been no research that attempts to model this index using non-linear Bayesian approaches and time-varying parameters simultaneously; such an approach has not yet been adopted.

Literature Review

The lack of tax revenue and non-payment of taxes pose significant challenges to the development of countries. In recent years, the tax gap has widened in both developing and developed countries. The tax gap is defined as the difference between the taxes that are legally owed and the amount of tax actually collected. Non-compliance with tax laws by both taxpayers and tax officials is a fundamental issue in emerging and developing economies. Tax audit is one of the methods employed to achieve the necessary compliance with tax laws (Aia et al., 2016). Combating tax evasion is a fundamental objective of all global tax systems, for which there are generally two basic strategies. One strategy is the establishment and enhancement of reliable self-assessment systems, and the second is the implementation of risk-based tax audits (Dehghani Doyle, 2019). Therefore, the primary objective of this study is to develop a model aimed at enhancing the quality of tax audits.


The research focuses on the tax files of all taxpayers, both individuals and legal entities, which have been audited by the Mazandaran province tax organization between 2010 and 2021. The sample comprises information extracted from tax files of taxpayers with files valued at 10 billion Rials and above. This threshold of 10 billion Rials was set to exclude small taxpayers, who generally do not have a substantial information burden, thus focusing on a more specific level of taxpayers. Following interviews with experts from the tax organization and university professors, and a review of past research, a total of 64 factors influencing the quality of tax audits were identified. These factors were categorized into three main groups: macro variables, characteristics of taxpayers, and characteristics of tax auditors. BMA approach has been used in this research.


From the viewpoint of tax audit service providers, establishing strategies to enhance the quality of tax audits is essential. This includes creating and reinforcing facilities systematically, conducting joint and integrated audits, and defining mechanisms to ensure auditors' independence. To effectively implement these strategies, it is crucial to consider the various dimensions of factors that affect the quality of tax audits. To achieve this objective, information on the indicators of the 64 factors affecting the quality of tax audits was input into three models: BMA, TVP-DMA and TVP-DMS. Based on the error rate, the BMA model demonstrated the highest level of accuracy. Following the model estimation, 17 main variables were identified. These variables include: the quality of tax audit of the past period, job experience, whether the case should be handled individually or as a group, auditor expertise, the extent of auditors’ use of received information, auditor’s work pressure, transactions with related parties, the presence of unofficial invoices, using other people’s business cards, accrued profit management, debt ratio, inflation, unofficial exchange rate, tax complexity, tax fairness, business climate index, and social capital index.
Based on the results of the research, the following suggestions are proposed:

Mechanization of all tax audit processes.
Establishing an integrated system of a smart database of circulars, instructions, and regulations.
Implementing measures and efforts to provide all tax auditors with access to the financial and economic microdata of taxpayers.
Development and implementation of integrated tax audit software across all sources.
Emphasizing the quality and substance of the content in issued tax audit reports.


The identified variables are divided into three main categories: tax auditor variables (the quality of tax audit of the past period, job experience, whether the case should be handled individually or as a group, auditor expertise, the extent of auditors’ use of received information, auditor’s work pressure, transactions with related parties, the presence of unofficial invoices, using other people’s business cards), Internal variables (accrued profit management; debt ratio), and macroeconomic variables (inflation, unofficial exchange rate, tax complexity, tax fairness, business climate index and social capital index).


Given the scarcity of comprehensive research in the field of tax audit quality, a multifaceted model has been designed to address this gap. It provides a comprehensive perspective on the quality of tax audit. Focusing on all dimensions of tax audit quality fosters the development of a systemic perspective in this field. Expanding the systemic perspective is expected to enhance the efficiency of the tax audit system. This improvement in efficiency can lead to more effective tax collection across different economic sectors, ultimately contributing to broader economic development.


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